Magnetic damper



United States Patent MAGNETIC DAIWPER Hugh E. Riordan and Edward J.Hayes, Siiver Spring,

Md., assignors to the United States of America as represented by theSecretary of the Navy Application December 3, 1954, Serial No. $73, 35?

1 Claim. (Cl. Slit-93) The present invention relates generally todamping systems, and more particularly to an improved magneticarrangement for damping motion of a body.

The servo systems for use in missile control mechanisms requireextremely effective damping because the delays in carrying out a missilemaneuver corresponding to a particular command signal must be minimized.Typical prior existing magnetic dampers used in missile servo systemscomprised a disc of magnetic material mounted on a rotating shaft of thesystem with permanent magnets arranged about the disc. The rotation ofthe disc, which was arranged in the magnetic field thus created, wouldbe impeded by the eddy currents induced in the disc as it cut the linesof flux. To increase the damping eifect provided by this arrangement, itwas necessary to increase the radius of the disc and the size of themagnets. This resulted in an undesirable increase in the inertia of thedisc.

One of the objects of this invention is to provide a mag netic damperwhich has an improved relationship between the amount of damping and theinertia of the moving element.

Another object of this invention is to provide a magnetic damper havinga reduced moment of inertia.

Still another object of this invention is to provide an improvedmagnetic arrangement which is economical to manufacture and which isefficient and reliable in operation.

Other objects and many of the attendant advantages of this inventionwill be apparent by reference to the following detailed description,taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a top view of the magnetic damper; and

Fig. 2 is an enlarged side elevation with parts broken away.

In accordance with the invention, there is provided a magnetic damperwhich comprises a cylinder mounted on a rotatable shaft the motion ofwhich it is desired to damp. Permanent magnets are arranged adjacent thecylinder, with pole pieces interposed betwen the magnets and arranged toprovide a magnetic field havingf lines of flux that are cut by therotating cylinder, thereby inducing eddy currents in the cylinder whichoppose its rotation. Additional means including sleeves of magneticmaterial are positioned inside the cylinder to reduce the reluctance ofthe magnetic path so that the number of lines of flux cut by thecylinder is increased.

Referring to the figures of the drawing, the improved magnetic damperincludes a housing consisting of rectangular top and bottom plates and22, and opposed permanent magnets 46 and 48. The top and bottom plates20 and 22 can be secured to the magnets 46 and 48, by suitable means,such as screw members 23. A

cylinder 24 of material having a low electrical resistance is rotatablymounted within the housing 10 between the magnets by means of a web 26that has an aperture 28 therein to receive the end 29 of a shaft 30.

A hearing 32, provided in the top plate 20, rotatably supports end 31 ofthe shaft 30. A second bearing 34, mounted adjacent the end of a hollowcylindrical sleeve 36, rotatably supports the other end 29 of the shaft30. The sleeve 36 is formed of magnetic material, and is secured to thetop plate 20 by screws 38.

A spacer 40 is interposed between the bearing 34 and the web 26. A nut42, screwed on the threaded end 29 of shaft 30 and engaging the web 26,is utilized to retain the cylinder 24 on the shaft 30. A second sleeve44, substantially the same as sleeve 36, is mounted on the bottom plate22 by suitable means, such as screws.

The permanent magnets 46 and 48, previously referred to nearly surroundthe cylinder 24 to provide a magnetic field of the required strength. Tocomplete the magnetic path, a pair of pole pieces and 52 are insertedbetween the permanent magnets 46 and 48 and extend into close spacedrelation to said cylinder.

The path of the flux from each of the permanent magnets 46 and 48includes the pole pieces 50 and 52, the cylinder 24, and the sleeves 36and 44. Because of the length of the cylinder 24 and the correspondinglylarger permanent magnets 46 and 48 and pole pieces 50 and 52, a largernumber of lines of force are cut by the cylinder 24 than would be cut bya disc of comparable inertia, result ing in increased eddy currentsbeing induced in the cylinder 24. This arrangement, therefore, providesan improved damping effect, while the inertia of the cylinder 24 remainsat a value that is low relative to that of a disc.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings. It is, therefore, to beunderstood that Within the scope of the appended claim the invention maybe practiced otherwise than as specifically described.

What is claimed is:

A magnetic damper including a housing having top and bottom plates, apair of permanent magnets mounted in spaced confronting relation betweenthe plates and a pair of pole pieces mounted between the magnets; acylinder having a centrally disposed web, a pair of cylindrical sleevesfixed in opposed relation in the housing and extending within thecylinder, said sleeves being formed of magnetic material and saidcylinder being formed of low resistance material, and opposed ends ofthe sleeves confronting opposite faces of the web, and means rotatablymounting the cylinder in the housing in spaced relation to the polepieces, said means including a shaft extending through and fixed to saidweb and extending through one of said sleeves and said top plate, andbearings in said sleeve and top plate for journaling said shaft.

References Cited in the file of this patent UNITED STATES PATENTS469,800 Wood a Mar. 1, 1892 590,648 Pratt Sept. 28, 1897 1,098,753Podlesak June 2, 1914 1,298,465 Dean Mar. 25, 1919 2,622,707 Faus Dec.23, 1952 2,653,257 Sailer Sept. 22, 1953 FOREIGN PATENTS 446,159 GreatBritain Oct. 22, 1935

